1. Field of the invention
The present invention relates to battery packs (or battery modules) having a structure in which a plurality of battery cells is electrically connected in series.
2. Description of the Related Art
There is a conventional patent document, Japanese patent laid open publication NO. 2004-200017, which discloses a battery pack having a structure in which a plurality of battery cells is arranged, for example, in three rows and three columns. The battery cells are electrically connected in series.
In the structure of the battery pack disclosed in the conventional patent document, a first battery cell having a negative electrode terminal of the minimum voltage potential and a final battery cell having a positive electrode terminal of the maximum voltage potential are arranged at opposite ends in the same row or in the same column, respectively, on one surface of the battery pack.
The battery pack disclosed in the conventional patent document has a size reduction structure because the battery cells in the battery pack are arranged in three rows and three columns and the negative electrode terminal having the minimum voltage potential and the positive electrode terminal having the maximum voltage potential are formed at the same surface of the battery pack. This structure does not require any connection plate in order to arrange the negative electrode terminal having the minimum voltage potential and the positive electrode terminal having the maximum voltage potential on one end surface of the battery pack. It is therefore possible to decrease the total number of components forming the battery pack and to prevent the strength of the battery pack from being decreased by heat energy.
There is a recent demand and a requirement to promote a downsizing of a battery pack because a device has a limited mounting space in which the battery pack is mounted. Further, there is another demand to reduce the device itself in view of the downsizing.
In order to solve the recent demand of downsizing, the conventional patent document, Japanese patent laid open publication NO. 2004-200017, provides the battery pack having the structure in which battery cells are arranged in three rows and three columns. However, such a structure of the battery pack disclosed in the patent document is insufficient to meet the recent demand and strict requirement.